When an opening in tissue is created either through an intentional incision or an accidental wound or laceration, biological healing of the opening commences through the proximity of the opposed living tissue surfaces. If the opening is very large or if its location subjects the wound to continual movement, a physician will seek to forcibly hold the sides of the opening together so as to promote the healing process.
In the case of skin tissue, for example, healing occurs best when the opposing dermal layers of the skin tissue are held in tight, primary proximity with each other. Human skin tissue is comprised of three distinct layers of tissue. The epidermal layer, also known as the epidermis, is the outermost layer and includes non-living tissue cells. The dermal layer, or dermis, is the middle layer directly below the epidermal layer and comprises the living tissue of the skin that is the strongest of the three layers. The subcutaneous, or hypodermis layer, is the bottom layer of skin tissue and includes less connective tissue, making this the weakest layer of skin tissue.
The most prevalent method for forcibly closing a tissue opening is through the use of a suture or “stitches.” As early as the second century, the Greeks were using sutures to physically close skin openings. In its simplest form, a suture is simply a length of material that is attached to a tissue-piercing device, such as a needle, and looped through the opposing sides of a tissue opening. The suture is then pulled tight and the loop closes, causing the opposing sides of the tissue opening to come into close physical contact. The suture loop is held tight by the tying of a knot, or knots, or some other locking mechanism. The first sutures were made of animal gut. Eventually other natural suture materials including leather, horsehair, flax, cotton and silk came into use. As the sciences of medical and materials technology have advanced over the course of the past century, new bioabsorbable materials have been developed to further improve upon the basic suturing concept.
While traditional suturing remains a popular method of effectuating closure of skin openings, the use of fasteners, for example staples and staplers, as a skin closure technique has become increasingly popular, especially in surgical settings where the opening is created through a purposeful incision. In these settings, the incision tends to make a clean, straight cut with the opposing sides of the incision having consistent and non-jagged surfaces. Typically, stapling of a skin opening, for example, is accomplished by manually approximating the opposing sides of the skin opening and then positioning the stapler so that a staple will span the opening. The stapler is then manipulated such that the staple is driven into the skin with one leg being driven into each side of the skin opening and the cross-member of the staple traversing the skin opening. Generally, the staple is made of a deformable material such as surgical stainless steel and the legs of the staple are driven into an anvil causing the staple to deform so as to retain the skin tissue in a compressed manner within the staple. This process can be repeated along the length of the opening such that the entire incision is held closed during the healing process.
The earliest medical staple designs were manufactured of metal and designed to deform aroand the captured tissue. Examples of these staples include U.S. Pat. Nos. 2,684,070, 3,273,562 and 4,485,816. Although effective, metal staples suffer from the drawback of requiring post-operative removal. As the science of medical polymers developed, staple designs incorporating bioabsorbable materials became available. The use of these bioabsorbable materials eliminated the need for post-operative removal of the staples. Examples of these staples include U.S. Pat. Nos. 4,317,451, 4,741,337, 4,839,130 and 4,950,258. Due to the nature of bioabsorbable polymers; however, bioabsorbable staples could not be inserted with the same deformation approach used by metal staples. In fact, bioabsorbable staples were purposefully designed to avoid any deformation requirement, as deformation was seen as a potential failure mechanism. An example of such a design is illustrated by the inwardly biased skin fastener of U.S. Pat. No. 5,089,009. Thus, as the physical and chemical properties of bioabsorbable surgical staples evolved, the development of designs and insertion methods associated with bioabsorbable staples have focused on avoiding deformation of the bioabsorbable fastener.
One potential use for bioabsorbable fasteners is in the subcuticular application of such fasteners for use in closing skin wounds as shown, for example in a series of patents to Green et al. in U.S. Pat. Nos. 5,292,326, 5,389,102, 5,423,856, 5,489,287 and 5,573,541. These patents disclose the use of a bioabsorbable, rod-like fastener inserted in a subcuticular manner to assist the healing process. Another bioabsorbable fastener design contemplated for subcuticular wound closure is U.S. Pat. No. 5,618,311 to Gryskiewicz, in which a more traditional staple design is promoted.
If they could effectively retain tissue, the bioabsorbable staples of these designs would have many advantages over conventional metal staples, such as no visible scarring and no need for subsequent removal by a physician. Unfortunately, none of the designs for bioabsorbable staples to date has been incorporated into a medically or commercially efficacious fastener. It would be desirable to provide a bioabsorbable fastener for use in wound closure that could achieve the advantages of a bioabsorbable material and still provide for an efficacious wound closure.